Technical Field
The present invention relates to a body motion detection device and a body motion detection method for detecting a body motion of a subject during an imaging operation using a radiographic image. The present invention also relates to an analysis point setting device and an analysis point setting method for setting analysis points for body motion detection on a radiographic image.
Background Art
When a radiographic image of a subject is obtained by imaging the subject by applying radiation, such as an x-ray, to the subject, the obtained radiographic image may be blurred and the image quality may be degraded due to a body motion of the subject during the imaging operation. In particular, when the imaged body part is the neck, the chest, the abdomen, the lumbar, etc., which requires a long exposure time, or the subject is a child, the rate of occurrence of body motion is relatively high, and degradation of the obtained radiographic image is a problem.
The technologist who carries out an imaging operation can determine whether or not there is a body motion of the subject by observing the subject during the imaging operation and immediately checking the obtained radiographic image. However, since a monitor provided in an imaging room has low resolution and a reduced image of the radiographic image is displayed on the monitor, and the observation environment is often relatively bright, it is difficult to determine whether or not there is a body motion by observing the displayed radiographic image. In such a situation, one may consider enlarging the radiographic image; however, the operation to enlarge the radiographic image decreases the efficiency of the workflow of the technologist.
In order to address this problem, techniques to automatically detect a body motion based on a radiographic image have been proposed. For example, a technique involving learning degradation of edges contained in radiographic images as feature quantities in two directions, the vertical direction and the horizontal direction, extracting an edge from a radiographic image, and determining whether or not the radiographic image is blurred due to a body motion based on the learned feature quantities and the extracted edge has been proposed (see U.S. Pat. No. 7,899,229, hereinafter Patent Literature 1). Also, a technique involving learning feature points with respect to a specific body part, which is a side of the head, and detecting a body motion in an obtained radiographic image using the results of the learning has been proposed (see H. Luo et al., “Motion blur detection in radiographs”, Proc. of SPIE, Vol. 6914, No. 69140U, pp. 69140U-1-69140U-8, 2008, hereinafter Non-Patent Literature 1).
In order to detect the above-described body motion, it is necessary to set analysis points on a radiographic image on which body motion detection is performed. To this end, the technologist may manually set the analysis points on a displayed radiographic image to perform body motion detection. Alternatively, a technique for automatically extracting, as the analysis points, part of pixels of a high spatial frequency part for body motion detection has been proposed (see Japanese Unexamined Patent Publication No. 2005-205086, hereinafter Patent Literature 2).